The horrific moment a mother saw her friend killed by a falling tree branch at Kew Gardens was recounted at an inquest today.

New Zealander Erena Wilson, 31, from Hanwell, was walking in the Royal Botanical Gardens when a large branch fell and killed her on September 23, 2012.

Ms Wilson had been visiting the gardens with friends, including Tess Marshall, who was celebrating her daughter Ruby’s third birthday with family.

The inquest, which began at West London Coroner's Court today and is expected to last until Friday, heard it had rained heavily on the day of the incident.

Ms Marshall told the inquest she had screamed at her friend after hearing "a loud crack like lightning" above them as they walked and chatted together.

She said: "Erena and I were walking together on the patch just chatting then, all of a sudden, I hear a loud crack like lightning, look up to my left and I see a broken tree.

"A whole load of foliage falling towards my head and all I could see was an umbrella of branches - I screamed and yelled at Erena, I ran and thought the whole tree was falling over.

"I heard a heavy thud of branches dropping and when I turned round, I could see Erena lying face down on the ground.

"I could see there was blood coming out of her ears and her mouth."

She said she yelled her friend's name and screamed "call an ambulance" before calling the emergency services on her mobile phone.

She added: "My three-year-old was very upset and crying."

John McLinden QC told the inquest it was a fluke nobody else was hurt, referring to how Ms Marshall's daughter had walked on ahead when her mother "could have easily been carrying her".

Ms Wilson's family remained in New Zealand and did not attend the inquest.

The inquest was postponed from October when coroner Elizabeth Pygott asked for further information relating to the natural phenomenon, known as summer branch drop, when tree branches fall suddenly after long dry spells followed by heavy rain.

Tony Kirkham, head of arboretum and horticultural services at Kew for 13 years, told the inquest he did not believe it to be the reason for the branch collapsing.

He said: "I don't attribute it to purely summer branch drop. First of all, with summer branch drop, we usually see it in summer months and this was at the end of September.

"It occurs on a very calm day with no wind usually and high humidity.

"I think it was the combination of water on the branches after heavy rain and I think we said the wind was 30mph, which is strong enough to move branches."

He added that the large cedar of Lebanon tree was one of the originals planted in 1759 when the gardens opened but was "still a healthy tree".

Warning signs were not displayed on the day and Mr Kirkham said there was no doubt over opening the tourist destination on the day of Ms Wilson's death.

The post-mortem examination was carried out on September 25, 2012, and found Ms Wilson suffered bruising on the left side of her scalp and an extensive brain injury before being pronounced dead at 2.51pm.

One juror was dismissed today because he is an employee of Royal Botanical Gardens.